The present invention relates to a tip turbine engine, and more particularly to a non-metallic composite tailcone for the tip turbine engine.
An aircraft gas turbine engine of the conventional turbofan type generally includes a forward bypass fan and a low pressure compressor, a middle core engine, and an aft low pressure turbine all located along a common longitudinal axis. Air flows into the engine at an inner diameter and an outer diameter of the engine. Air entering through the outer diameter of the engine exits the rear of the engine at the outer diameter as a relatively low temperature gas stream after flowing through the bypass fan.
Airflow entering the inner diameter of the engine enters a high pressure compressor driven by a high pressure turbine to compress the air to a high pressure. This high pressure air is then mixed with fuel in a combustor and ignited to form a relatively high temperature gas stream. The high temperature gas stream flows axially aft to rotatably drive the high pressure turbine which rotatably drives the high pressure compressor through the high pressure shaft. The high temperature gas stream leaving the high pressure turbine is expanded through the low pressure turbine which rotatably drives the bypass fan and low pressure compressor through a low pressure shaft. The high temperature gas stream exits the rear of the engine at the inner diameter from the low pressure turbine and flows over a tailcone. The tailcone is made of titanium or other metal to withstand the elevated temperatures of the high temperature gas stream.
Although highly efficient, conventional turbofan engines operate in an axial flow relationship where airflow essentially travels linearly through the engine. The axial flow relationship results in a relatively complicated elongated engine structure of considerable length relative to the engine diameter. This elongated shape may complicate or prevent packaging of the engine in particular applications.
A recent development in gas turbine engines is the tip turbine engine. Tip turbine engines locate an axial compressor forward of a bypass fan which includes hollow fan blades that receive airflow from the axial compressor therethrough such that the hollow fan blades operate as a centrifugal compressor. Compressed core airflow from the hollow fan blades is mixed with fuel in an annular combustor that is radially outward from the fan blades and near an outside diameter of the tip turbine engine. The airflow and fuel mixture is ignited to form a relatively high temperature gas stream which drives the turbine integrated onto the tips of the hollow bypass fan blades for rotation therewith as disclosed in U.S. Patent Application Publication Nos. 2003192303; 20030192304; and 20040025490. Unlike conventional engines, the relatively high temperature gas stream exits the rear of the tip turbine engine at the outside diameter, while the relatively low temperature gas stream flowing through the bypass fan exits the rear of the tip turbine engine at the inner diameter and flows over the tailcone.
Accordingly and because of the low temperature gas stream discharged from the inner diameter in a tip turbine engine, it is desirable to provide a lighter, non-metallic tailcone in the tip turbine engine.